The present invention relates generally to piezoelectric motors. More particularly, the present invention relates to a piezoelectric motor coupled to a driver configured to compensate for temperature and voltage variations, and to tune to a predetermined drive frequency and a selected power output.
Accurate micro-positioning and actuation are often required in certain applications, such as slide positioning systems. Piezoelectric drivers have been utilized to replace leadscrews and gears typically used in such slide positioning systems. The piezoelectric drivers use a piezoelectric material to convert an electrical field applied to the piezoelectric material to mechanical displacement, or a dimensional change in the piezoelectric material. Thus, the piezoelectric material may be affixed to a first member, such as the base of a slide, and engage or bear against a second member, such as the platform of the slide. The piezoelectric material may be oriented such that the dimensional change, or expansion and contraction, of the piezoelectric material due to the applied electrical field causes the second member to move with respect to the first member.
Some piezoelectric motors use a pair of engaging elements which are selectively clamped to translate a housing relative to a separate member. The piezoelectric driving elements are each coupled to one of the engaging elements. The piezoelectric driving elements selectively expand and contract in response to an applied voltage of selected magnitude and frequency. Thus, the piezoelectric driving elements produce a variable driving force between the housing and the engaging elements, and which is conducted through the engaging elements to apply a variable clamping force to the separate member. The engaging elements are responsive to the expansion and contraction of the piezoelectric driving elements to selectively inhibit and impart relative motion between the housing and the separate member to produce motion.
Some advantages of piezoelectric motors include precise positioning (i.e. nanometer precision), efficiency, lack of backlash, and quiet operation. However, despite these advantages, several disadvantages still exist with piezoelectric motors, and other commercially available micro-motors.
Piezoelectric motors are actuated by microprocessor drivers that control power magnitude and frequency to the motor. Each piezoelectric motor has a resonant frequency at which performance is optimized, and thus each driver and motor (or motor set) must be tuned to its resonant frequency after installation into an application. This tuning is typically accomplished by manually calibrating the output frequency and voltage magnitude of the motor. Manual calibration is tedious, time consuming and prone to human error resulting in less than optimal performance by the motor.
Additionally, piezoelectric motors often need retuning during or after use. Temperature and voltage changes can affect the optimal resonant frequency of operation. Consequently, retuning is required to ensure optimum performance of the motor.
Another disadvantage is that power levels must be tuned according to the number of motors being driven in parallel. Thus, changing the number of motors being driven requires recalibration of the driver.